Successful renal transplantation is the preferred therapeutic modality in children with end-stage renal disease (ESRD), but there are a number of immunologic barriers to this goal. Pre-transplant blood transfusions can diminish transplant rejection; the mechanism is not known. In an attempt to improve the availability and success of transplantation, we will employ 2 transfusion protocols. In each, we will probe specific immunologic variables which may account for the beneficial transfusion effect. Protocol I: Potential cadaver transplant recipients will be randomized to either a group receiving 5 full transfusions (10 cc/Kg body weight) over 5 months or a group receiving 20 small-dose (2.5 cc/Kg body weight) transfusions over the same time period. Each transfusion in both groups will come from "identified" donors who will be available for subsequent study. Graft outcome and immunologic parameters will be compared between groups. Protocol II: ESRD patients with high levels of anti-HLA antibodies will receive weekly transfusions of blood from donors against whom they are presensitized, in an attempt to induce secondary unresponsiveness and disappearance of the antibodies. This may allow us to successfully transplant these otherwise untransplantible ESRD patients. We will also extend this procedure to patients who have developed anti-HLA antibodies against a potential transplant donor after donor-specific transfusions. At specified times, we will study the following immunologic parameters: lymphocytotoxic antibodies against B and T cells of a panel and the specific blood donors at multiple incubation temperatures; autolymphocytotoxic antibody; immune complexes; enumeration of T cell subsets including total, "active", suppressor/cytotoxic and inducer subsets; specific suppressor cells in mixed lymphocyte reaction; immunoglobulin secreting cells; and spontaneous blastogenesis. Three potential long-term objectives are sought: 1) to learn the optimal way of using transfusions to enhance transplant success; 2) to improve availability and success of renal transplantation to highly presensitized ESRD patients; and 3) to learn the relevant immunobiologic parameters of transfusion which are associated with improved renal transplant outcome.